Most condensing components currently used in miner's helmet LED lamps adopt parabola-shaped reflectors or total-reflection secondary optical lens to converge light emitted from LED.
For miner's helmet LED lamps using total-reflection secondary optical lens, as shown in FIG. 1, when a current lens with a diameter of 20 mm-30 mm is fitted with a 1-3 W LED with a 1 mm×1 mm chip, usually the minimal beam angle that can be obtained is about 8°-10°, which makes it impossible to produce an illuminance of 4,000-6,000 Lux at a distance of 1-3 meters. In order to meet the said illuminance requirement, usually at least 3 to 4 LEDs are needed, which makes it fast for batteries to be used up when the lamps operate for a long period of time. For a single LED, to meet the said illuminance requirement, its beam angle has to be kept below 5°. Nevertheless, to realize a beam angle below 5°, the diameter of the lens has to be increased to more than 50 mm-60 mm. If the total-reflection lens structure as shown in FIG. 1 is adopted, the thickness of the lens will have to be greatly increased. In such a case, the lens will have a large shrinkage during the process of injection molding, making injection molding very difficult to realize. Moreover, with the increase of the thickness of the lens, the weight of the lens will be increased greatly as well.
Therefore, at present, a kind of optical lens that can output beams at a narrow angle is urgently needed.